Method of Reducing Fuel Corrosiveness

ABSTRACT

Fuels containing biodiesel, petroleum distillates, or blends of these may be treated by the addition of small amounts of one or more alkanolamines according to formula (I) 
       R n —N(CH 2 CHR 1 OH) 3-n  ;   (I) 
     wherein n is 1 or 2, R 1  is H or CH 3 , and each R is independently selected from the group consisting of hydrogen and branched, linear, and cyclic C3-C24 alkyl groups, provided that at least one R is not hydrogen. Fuels treated in this manner may be less corrosive toward metals with which they are in contact.

FIELD OF THE INVENTION

The invention relates to fuel oils. More particularly, it relates tofuel oils containing additives that reduce corrosion in systems incontact with the oils.

BACKGROUND OF THE INVENTION

Fuel oils are widely used in a variety of applications, including dieselengines, furnaces, jet engines, and other energy-consuming uses.Traditional fuel oils are well known, and are produced by refining crudepetroleum feedstocks via distillation, cracking, and other processes.However, the crude petroleum feedstocks are in limited supply and arenon-renewable, and therefore renewable sources of fuel oils areincreasingly sought.

One renewable fuel oil source is biodiesel, a clean-burning alternativefuel produced from domestic, renewable resources. Biodiesel contains nopetroleum, but it can be blended at any level with petroleum diesel tocreate a fuel blend. It can be used in compression-ignition (diesel)engines with little or no modification. Biodiesel is biodegradable,essentially nontoxic, and essentially free of sulfur and aromaticcompounds, and thus can provide certain environmental advantages.

Biodiesel is essentially a mixture of methyl and/or ethyl esters offatty acids, made through transesterification of fatty acidtriglycerides (oils) with methyl or ethyl alcohol. The most commonlyused raw material oils are triglyceride seed oils (e.g., soybean oil,palm oil, rapeseed oil). Biodiesel esters are never produced as 100%pure compounds, and one common impurity in biodiesel is free fattyacids, which can lead to corrosion problems.

Biodiesel may be used alone, petroleum oils may be used alone, or blendsmay be used. Petroleum oils typically also contain some amount of acidicimpurities, especially naphthenic acids. Acids from either source maycause any of a number of problems, including corrosion, poor combustion,elevated pour points, formation of deposits, and poor lubricity. As aresult, fuel producers typically try to reduce the acidity of theirproducts, but doing so usually introduces additional costs for theseproducts, which generally sell at low margins. Beyond a certain point,the removal of acids becomes economically unacceptable, and thereforecrude petroleum oils with too high a naphthenic acid content orbiodiesel feed with too high a free fatty acid content become aliability to the fuel producer. Thus it would be beneficial to provideeconomical ways of dealing with free acids in fuel oils.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a treated fuel. The treated fuelincludes:

-   -   a) an untreated fuel consisting of a biodiesel, a petroleum        distillate, or a blend thereof; and    -   b) one or more alkanolamines according to formula (I)

R_(n)—N(CH₂CHR¹OH)_(3-n)   (I);

wherein n is 1 or 2, R¹ is H or CH₃, and each R is independentlyselected from the group consisting of hydrogen and branched, linear, andcyclic C3-C24 alkyl groups, provided that at least one R is nothydrogen, and wherein the treated fuel is essentially free of addedbiological control agents.

In another aspect, the invention provides a method of treating a fuelcomprising blending together an untreated fuel consisting of abiodiesel, a petroleum distillate, or a blend thereof and one or morealkanolamines according to formula (I) as shown above, wherein thetreated fuel is essentially free of added biological control agents.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, fuels may be treated by the addition ofsmall amounts of one or more alkanolamines according to formula (I)

R_(n)—N(CH₂CHR¹OH)_(3-n)   (I);

wherein n is 1 or 2, R¹ is H or CH₃, and each R is independentlyselected from the group consisting of hydrogen and branched, linear, andcyclic C3-C24 alkyl groups, provided that at least one R is nothydrogen. In some embodiments of the invention, the total number ofcarbon atoms in the R group(s) taken together is from 4 to 24, and insome preferred embodiments the number is from 6 to 20. Without wishingto be bound by any particular theory or explanation, it is believed thatthe presence of a significant amount of hydrophobic substitutiondirectly on the amine nitrogen is beneficial to the reduction ofcorrosion. Exemplary useful alkanolamines of formula (I) includebutyidiethanolamine, butylaminoethanol, dibutylaminoethanol,diisopropylaminoethanol, octylaminoethanol, and octyldiethanolamine.

The alkanolamine(s) of formula (I) may be incorporated into the treatedfuel in any amount. Typically, they will be present in an amount equalto at least 0.8 mol equivalents relative to a total of the fatty andnaphthenic acid impurities, and typically in an amount equal to from0.01 to 2 wt % relative to the untreated fuel, more typically from 0.01to 1 wt %. It is to be understood that, when reference is made to atreated fuel containing a certain amount of an alkanolamine of formula(I), this includes both alkanolamine that is unreacted and that whichhas formed a salt (but not an ester or amide) with fatty, naphthenic, orother acid impurities present in the untreated fuel. At least 95 wt % ofthe alkanolamine(s) of formula (I) added to the untreated fuel isunreacted or in the form of a salt, and preferably at least 98%.

Fuels to be treated with the alkanolamines of formula (I) includebiodiesel, petroleum distillates, and blends of these. In someembodiments, the blends contain at least 5 wt % of biodiesel, or theymay consist of a blend in which the biodiesel constitutes at least about20 wt % of the blend, or at least about 80 wt % of the blend, with thebalance being a petroleum distillate. Biodiesel derived from any naturalor synthetic fat or oil is suitable for treatment according to theinvention.

Petroleum distillates suitable for use according to the inventioninclude any of a variety of petroleum-based fuels, including but notlimited to those normally referred to as “diesel.” Exemplary distillatesmay include gasoline, gas-oil, and bunker fuel. Petroleum middledistillates will be used in many applications, and such middledistillates include mineral oils boiling within the range from 120 to450° C. obtained by distillation of crude oil, for example standardkerosene, low-sulfur kerosene, jet fuel, diesel and heating oil such asNo. 2 fuel oil. Exemplary distillates that may be blended with biodieselfor treatment with the alkanolamines of this invention are those whichcontain not more than 500 ppm, in particular less than 200 ppm, ofsulfur and in specific cases less than 50 ppm of sulfur or even lessthan 5 ppm. Generally, the petroleum distillate may comprise from 0.01to 1 wt % of the naphthenic acids, but the invention is not limited tothis range. Useful distillates, especially middle distillates, aregenerally those which were subjected to refinement under hydrogenatingconditions and which therefore contain only small amounts ofpolyaromatic and polar compounds that impart natural lubricatingactivity to them. The alkanolamines according to the invention may alsofind good use in those distillates that have 95% distillation points ofless than 370° C., in particular 350° C. and in special cases less than330° C.

The untreated fuel typically contains a minor amount of one or morefatty acids and/or naphthenic acids as impurities, although it need notcontain either of them. Thus, in some embodiments, the untreated fuelmay consist essentially of those impurities and the esters orhydrocarbons of the fuels themselves. In the case of biodiesel, theacids will typically be fatty acids, while naphthenic acids may often befound in petroleum distillates. The amount of fatty and/or naphthenicacids present in the untreated fuels is typically from 0.01 to 5 wt %,more typically from 0.01 to 2 wt %, and most typically between 0.05 and1 wt %.

An untreated fuel may consist essentially of the biodiesel and/or thepetroleum distillates, along with their acid impurities, or it may alsocontain other optional additives such as those detailed below.Similarly, the treated fuel may consist essentially of the untreatedfuel combined with one or more alkanolamines of formula (I), or it mayalso contain those other additives. It should be noted that certainadditives, when used in combination with the alkanolamine(s), may have asubstantial effect on certain important properties of the treated fuel.Such properties include the viscosity of the treated fuel at 35° C. (ormore generally, at engine operating temperature), the pour point of thetreated fuel, the rate or extent of rust formation or other corrosion ofmetals in contact with the treated fuel, and the growth of bacteria,molds, fungi, slimes, and other microbial forms in the fuel. The effectsof such changes may or may not be desirable in a given situation, andtherefore some embodiments of the invention preclude the use of suchadditives in an amount that materially affects one or more of theseproperties.

Examples of materials that may have a material effect on one or more ofthe above-mentioned properties, when used in a high enough amount incombination with the alkanolamines of formula (I), include esters oramides of the alkanolamines of formula (I) with fatty or naphthenicacids, and polymers containing vinyl ester and olefin repeat groups.Other such materials include carboxylic acid esters of alkoxylatedphenol-aldehyde resins, and certain biological control agents. Examplesof the latter include certain triazines, thiazolinones, halogenatedcompounds, thiocyanates, carbamates, pyrithiones, quaternary ammoniumcompounds, aldehydes, heterocyclic compounds, soluble metal ions andreactive alkylating agents. Specific examples of biological controlagents that may or may not be included in an effective amount include1,3,5-(2-hydroxyethyl)-s-triazine and benzoisothiazolone.

As distinct from the foregoing list of additives, certain otheradditives may typically be included in the treated fuel in an amountsufficient to achieve certain performance advantages. For example,surfactants may be included to help reduce the buildup of deposits.Other ingredients might also include fatty acids as friction modifiers,octane boosters, cetane enhancers, and explosion suppressors (e.g.,tetraethyllead or manganocene tricarbonyl). Water may also be present inthe treated fuel. If present, it may be in only small amounts, i.e., atless than 2 wt % or even less than 0.5 wt %, most typically less than500 ppm. It may however be present in larger amounts, for example from 2to 25 wt % based on the total weight of the resulting mixture, morecommonly 10 to 15 wt %, in the form of a solution, stabilized emulsion,or other dispersion.

The alkanolamines of formula (I) may simply be blended with fuel,without any heating or other special processing steps. Thus they may beblended at ambient temperatures, although lower or higher temperaturesmay be used as long as mixing is reasonably facile and undesiredreactions do not occur. Typically, the temperature will be from 10 to50° C. The pH of the fuel will be increased by the addition of theamine, and the corrosion-reducing effect of the alkanolamine will berealized following the addition. It should be noted that the measuredacid number of the fuel will not necessarily change after thealkanolamine is added, since titration in the usual manner (with KOH)may still pick up protons bound by amino nitrogen. However, even thoughthe fuel's acid number does not decrease as much as it would if astronger base were used instead of the alkanolamine, the fuel stillshows marked reduction in corrosiveness. Therefore, in some cases,producers may wish to modify their specification test to account for thefact that amine neutralizing agents are being employed.

Treated fuels according to the invention generally provide relativelylow rates of corrosion, making them suitable for use in a number ofapplications. For example, many applications involve the use of brassparts, either leaded or unleaded, and corrosion caused by some prior artfuels can lead to excessive and deleterious levels of copper and othermetals in the fuel. Low corrosion of copper, brass and iron is animportant property for many fuels, and such low corrosion isparticularly important in biodiesel type fuels, since these fuels needto be compatible with existing engines that contain iron, iron alloy,aluminum alloy, copper, and copper alloy parts. Corrosion of brass inthe presence of the treated fuel may produce less than 70 ppm of copperin the treated fuel, as measured by the test methods described inExample 1 below. Without wishing to be bound by any particular theory orexplanation, it is believed that the alkanolamines of formula (I)neutralize at least some of the free acids, and that this reducescorrosion.

EXAMPLES Example 1 Corrosion Inhibition in Aqueous Solutions ofAlkanolamine and Fatty Acid

The following data provide an indication of corrosion performance insituations where diesel fuel is exposed to pools of standing water(e.g., fuel tanks, storage containers) and the fatty acids and amineswithin the fuel are extracted into the pools. Eight aqueous solutionseach containing a different alkanolamine at a concentration of 0.3 Malong with octanoic acid at a concentration of 0.2 M and with the pHadjusted to 8.5 (at room temperature) by H₃PO₄ and/or KOH addition wereprepared as models of heavily neutralized biodiesel type fuel. A450-gram portion of each of these solutions was weighed carefully andtransferred to a wide-mouth screw-cap glass bottle. Brass panels(2″×2″×0.032″) panels were washed with 10% liquid-Nox (Alcanox), buffeddry with a paper towel, and immersed in the solutions described above.Caps were placed tightly on all bottles to insure that no evaporationtook place. A 5-gram sample of each solution was collected after 30 daysand analyzed by ICP (Inductively Coupled Plasma) atomic emissionspectroscopy for metals content. Two types of brass were tested—leaded(CA-360, 3% Pb) and unleaded (CA-260) alloy. The results (passivedissolution of copper, zinc and lead) are shown below.

Day 30, Alkanolamine & Octanoic Acid, Unleaded Brass

Alkanolamine Cu (ppm) Pb (ppm) Zn (ppm) Alkanolamines of formula (I)Butylaminoethanol 10 <0.02 7 Butyldiethanolamine 44 <0.02 9Diisopropylaminoethanol 2 <0.02 0.8 Isopropylaminoethanol 44 <0.02 16Prior Art Alkanolamines 2-Amino-2-methyl-1-propanol 123 <0.02 66Diglycolamine 234 <0.02 19 Monoethanolamine 211 <0.02 14 Triethanolamine171 <0.02 3

Day 30, Alkanolamine & Octanoic Acid, Leaded Brass

Alkanolamine Cu (ppm) Pb (ppm) Zn (ppm) Alkanolamines of formula (I)Butylaminoethanol 9 0.2 5 Butyldiethanolamine 66 0.7 12Diisopropylaminoethanol 1 0.06 0.6 Isopropylaminoethanol 19 0.3 7 PriorArt Alkanolamines 2-Amino-2-methyl-1-propanol 74 1 37 Diglycolamine 1682 31 Monoethanolamine 134 2 4 Triethanolamine 165 7 2

As can be seen from the results shown in the above tables, solutionscontaining fatty acids (i.e., octanoic acid) and the alkanolamines ofthis invention have far less tendency to corrode brass than do solutionsin which prior art alkanolamines are used instead.

Although the invention is illustrated and described herein withreference to specific embodiments, it is not intended that the subjoinedclaims be limited to the details shown. Rather, it is expected thatvarious modifications may be made in these details by those skilled inthe art, which modifications may still be within the spirit and scope ofthe claimed subject matter and it is intended that these claims beconstrued accordingly.

1. A treated fuel comprising: a) an untreated fuel consisting of abiodiesel, a petroleum distillate, or a blend thereof; and b) one ormore alkanolamines according to formula (I)R_(n)—N(CH₂CHR₁OH)_(3-n)   (I); wherein n is 1 or 2, R¹ is H or CH₃, andeach R is independently selected from the group consisting of hydrogenand branched, linear, and cyclic C3-C24 alkyl groups, provided that atleast one R is not hydrogen, and wherein the treated fuel is essentiallyfree of added biological control agents.
 2. The treated fuel of claim 1,wherein the treated fuel comprises less than 2 wt % water.
 3. Thetreated fuel of claim 1, wherein the treated fuel further comprises from2 to 25 wt % water.
 4. The treated fuel of claim 1, wherein theuntreated fuel consists of said blend and wherein the biodieselconstitutes at least about 5 wt % of the blend.
 5. The treated fuel ofclaim 1, wherein the untreated fuel consists of said blend and whereinthe biodiesel constitutes at least about 20 wt % of the blend.
 6. Thetreated fuel of claim 1, wherein the untreated fuel consists of saidblend and wherein the biodiesel constitutes at least about 80 wt % ofthe blend.
 7. The treated fuel of claim 1, wherein the untreated fuelconsists of the biodiesel.
 8. The treated fuel of claim 1, wherein theuntreated fuel consists of the petroleum distillate.
 9. The treated fuelof claim 1, wherein the biodiesel or the petroleum distillate comprisesone or more fatty or naphthenic acid impurities, or both, and whereinthe one or more alkanolamines of formula (I) are present in an amountequal to at least 0.8 mol equivalents relative to a total of the fattyand naphthenic acid impurities.
 10. The treated fuel of claim 1, whereinthe one or more alkanolamines of formula (I) are present in an amountequal to from 0.01 to 2 wt % relative to the untreated fuel.
 11. Thetreated fuel of claim 1, wherein corrosion of brass in the presence ofthe treated fuel produces less than 70 ppm of copper in the treatedfuel.
 12. The treated fuel of claim 1, wherein the biodiesel or thepetroleum distillate comprises one or more fatty or naphthenic acidimpurities, or both, and wherein the biodiesel comprises from 0.01 to 5wt % of the fatty acid impurities.
 13. The treated fuel of claim 1,wherein the untreated fuel consists of said blend.
 14. The treated fuelof claim 1, wherein the petroleum distillate comprises No. 2 fuel oil.15. The treated fuel of claim 1, wherein the petroleum distillatecomprises a jet fuel.
 16. The treated fuel of claim 1, wherein thebiodiesel or the petroleum distillate comprises one or more fatty ornaphthenic acid impurities, or both, and wherein the petroleumdistillate comprises from 0.01 to 1 wt % of the naphthenic acidimpurities.
 17. The treated fuel of claim 1, wherein a total number ofcarbon atoms in the R groups is from 4 to
 24. 18. The treated fuel ofclaim 1, wherein a total number of carbon atoms in the R groups is from6 to
 20. 19. A method of treating a fuel, comprising blending together:a) an untreated fuel consisting of a biodiesel, a petroleum distillate,or a blend thereof; and b) one or more alkanolamines according toformula (I)R_(n)—N(CH₂CHR₁OH)_(3-n)   (I); wherein n is 1 or 2, R¹ is H or CH₃, andeach R is independently selected from the group consisting of hydrogenand branched, linear, and cyclic C3-C24 alkyl groups, provided that atleast one R is not hydrogen, and wherein the treated fuel is essentiallyfree of added biological control agents.
 20. The method of claim 19,wherein the blending is performed at a temperature from 10 to 50° C. 21.The method of claim 19, further comprising blending from 2 to 25 wt % ofwater, based on the total weight of the resulting mixture, with any ofthe biodiesel, the petroleum distillates, the untreated fuel, or thetreated fuel.